Off-line high-performance liquid chromatography and solid-phase extraction clean-up for confirmation of pesticide residues in fresh produce by gas chromatography mass spectrometry

GC-MS or GC-IT in conjunction with the GC-ECD, GC-FPD and HPLC Post-Column Derivatization for multiresidue scan analyses is a great complementary instrument for identification or confirmation purposes. However, MS in EI mode serves as a non-selective detector that is easily susceptible to interference by produce matrices in trace level residue analysis. The development of an effective clean-up method is essential. In this research, a combination of HPLC/C-18 and SPE/Florisil clean-up methods were used to reduce matrices in 10 commodities. Using the PBM system, the reference spectra of the computerized Anaheim data base were fingerprint matched to the fortified residues at the 50 ppb level. For most commodities, the PBM quality value was above 90% with the exception of whole oranges. The study demonstrates that the produce matrix of individual commodities varies considerably. The method met difficulties in the analysis of citrus due to the citrus peels. Although the method is commodity dependent, the clean-up procedure has reduced matrix interference in most cases. Efficiency is approximately in a range of 10(5) to 10(6) times, thus the method is effective in confirming trace level pesticide residues in fresh produce.